It may be hard to believe, but Pink swears she gained 55 pounds during pregnancy! The 33-year-old singer welcomed daughter Willow with husband Carey Hart in June 2011, and after indulging during pregnancy she hit the gym hard after giving birth.

Pink proudly flashes her flat, toned abs on the November cover of Shape magazine in black underwear, bra and a see-through tank top.

"I ate a lot of cheesecake during my pregnancy," she says. "Also anything sour—Sour Skittles, Sour Patch Kids, key lime pie..." But after waiting a few months to let her body recover from giving birth, she had celebrity trainers Jillian Michaels and Jeannette Jenkins get her back into shape.

"They both kicked my butt more than any other person I've ever worked out with," Pink explains of Biggest Loser's Michaels, 38, and Jenkins, the president of the Hollywood Trainer fitness company. And after losing the weight, Pink boasts she's now in the best shape of her life.